The present invention concerns the field of sighting or aiming instruments. Its subject matter is more particularly a device capable of determining the direction of a target in a predefined frame of reference, the device having sighting means and means for processing signals derived from the sighting means, the processing means being capable of determining the direction between the sighting means and the target and transmitting them to imaging means or to external means.
Numerous devices exist which are capable of determining, in particular, the elevation and azimuth of a target.
For example EP 557 591 describes a device capable of determining the orientation of an object with respect to a reference orientation, and comprises a movable orientation unit and a reference sensor unit, each one of them having a three-axis gyroscopic unit, a calculation unit receiving measured values from the aforesaid units, and an output unit.
Many of these devices require substantial logistics. However, in certain circumstances it may prove necessary or indeed vital to use a lightweight and manageable device that can be used by a single operator.
Such devices exist, and use magnetic field sensors.
Among these devices, the binoculars sold under the LEICA trade name are capable of determining the elevation and azimuth of a target, and give complete satisfaction when used outdoors. They cannot be used, however, in an environment having magnetic disturbances.
Other devices analyze electrostatic or electromagnetic fields and, by reading their cartography, determining the position and direction of a target.
The devices are satisfactory in environments which are completely known and of small dimensions. They are difficult to use, however, and do not tolerate changes in the electrical environment.
Also known is U.S. Pat. No. 4,012,989, which describes a helicopter having a device for determining the direction of a target so as to direct a movable weapon system. The device for determining the direction of a target has a movable sighting member equipped with two integrated inertial gyroscopes, resetting means integral with the helicopter equipped with two gyroscopes, and means for slaving the direction of the weapon as a function of the data supplied by the gyroscopes. The resetting means serve to immobilize the four gyroscopes in a first reference position to define a frame of reference. When the sighting means are disengaged from the resetting means, the four gyroscopes are released. The gyroscope pair integrated with the resetting means then rotates as a function of the movements of the helicopter. The gyroscope pair integrated with the sighting member rotates as a function of the movements of the helicopter and the movements of the gunner controlling the sighting member. The weapon is directed in real time toward the target as a function of the difference in rotation between the two gyroscope pairs.
This device has numerous drawbacks. For example, the gunner is obliged to keep the sighting means continuously pointed toward the target until the weapon system is fired, which limits firing capabilities and makes the helicopter vulnerable if multiple targets are present. Because of helicopter vibrations and uncontrolled wrist movement, the two gyroscopes of the sighting means transmit to the processing means sequences of signal changes which cause an accumulating measurement error which impairs the accuracy with which the target direction is determined. On a ship, if the sea is rough and there is thus severe pitching and rolling, it would be almost impossible to orient the weapon system toward the target with such a device.